Failure of tight junctions (T J) to function as physical barriers between the apical and basolateral membrane domains of cells allows growth signals to reach receptors that are normally occluded, a process that has been linked to metastasis of cancers. Several proteins have been identified that are important for forming the TJ. One of these complexes involves Par6, Par3, aPKCzeta, and the RhoGTPase, Cdc42, which has also been described to regulate the fidelity of basolateral targeting. We hypothesize that Par6, Par3, and aPKCzeta are effectors of Cdc42, and that dynamic interactions between these proteins regulate delivery and recycling of vesicles that carry transmembrane proteins to basolateral domains on the plasma membrane. We propose to test this hypothesis using established biochemical techniques, RNA interference, and state-of-the-art fluorescent imaging instruments available at Yale University. The results of these studies will identify the role of TJ resident proteins in polarized vesicular trafficking, and how differential delivery of cargo to domains on the plasma membrane function to maintain the TJ.